1. Field of the Invention
The present invention relates to bioactive cements used in medical and dental fields for bonding or fixing artificial biological materials, such as artificial bones or artificial teeth roots, etc., and which are also used as prosthetic materials for repairing defected portions of teeth or bones of living bodies.
2. Related Art Statement
Heretofore, in the fields of orthopedic surgery and dental surgery, when a portion of a bone is defected or cut away for the sake of bone fracture or bone tumor, etc., or when the bone of jaw is defected due to Riggs' disease or pulling out of a tooth, artificial biomaterials selected from metals, ceramics and crystalline glasses, etc., have been used to repair or remedy such defected portion.
Such artificial biomaterials are requested to adapt the shape of defected portion, and are desired quickly embedded and fixed in the defected portion. For that purpose, the defected portion has to be ground to meet the shape of the artificial biomaterial, otherwise the artificial biomaterial has to be worked to meet the shape of the defected portion. However, such grinding or working is quite difficult to perform precisely.
Therefore, when using the artificial biomaterials in living bodies, some cements have been used, in order to bond and fix the artificial biomaterials to bones or teeth of living bodies. For example, in the field of orthopedic surgery, cements made of PMMA (polymethylmethacrylate) has been widely used. In the field of dental surgery, cements made of zinc phosphate or carboxylate have been used. Moreover, granules of apatite or alumina ceramics have been directly filled in the defected portion so as to adapt the shape of the defected portion.
However, though the above-described various cements can firmly bond to the artificial biomaterials, they can not chemically bond to bones of living bodies. Thus, if the cement is used in the defected portion for a long period of time, the fixation between tooth or bone of living body and the cement is likely loosened. Moreover, granules of apatite or alumina ceramics do not bond with each other, so that they have to be fixed in the defected portion with the aid of the cement.
Recently, in consideration of the above situations, various bioactive cements have been reported which can chemically bond to bones of living bodies. This type of bioactive cements use crystalline powders of calcium phosphate, etc., alone or in admixture, which is/are reacted with a hardening liquid to precipitate crystals of hydroxyapatite, etc. The bioactive cements are classified into two types depending on the type of the hardening liquid. One type of bioactive cements is those that use an aqueous solution of citric acid or malic acid, etc., as the hardening liquid, and the other type of bioactive cements are those that use water as the hardening liquid. The former type of cements harden in a short time and exhibit high initial strength, so that quick and strong bonding and fixing of the artificial biomaterials by the cements can be expected. However, due to the use of the aqueous solution of the organic acid, they are, when used, likely to incur an inflammatory reaction to the surrounding tissue of living bodies, and has a problem in that the cements are likely deteriorated in living bodies due to their high degradation rate. Meanwhile, the latter type of cements do not use an organic acid, so that they do not incur an inflammatory reaction to the surrounding tissue of living bodies, however, they have slow hardening speed and hence low initial strength and can not attain practically necessary quick bonding and fixing of the artificial biomaterials to bones or teeth of living bodies.